1. Field of the Invention
This invention relates to control systems for stepper motors. More specifically, the invention is a control system and method for stepper motors that adjusts to motor loading in order to reduce internal power dissipation losses.
2. Description of the Related Art
Stepper motors are used in a wide variety of machines to provide digital control of moving parts. However, typical stepper motors exhibit several undesirable characteristics. Principal among these characteristics are: insufficient resolution due to a relatively low number of steps per revolution (e.g., 200 steps per motor revolution); a high ripple torque; and a high constant internal power dissipation regardless of motor load. While the resolution and ripple torque problems can be addressed by providing high resolution motor command signals, the problem of constant internal power dissipation has been a continuing source of power loss.
The internal power dissipation of stepper motor is a function of motor current I and the resistance R of a motor winding. Accordingly, if the stepper motor is driven by a constant current source, power dissipation (or I.sup.2 R) will remain constant regardless of the load on the stepper motor. As a result, the stepper motor generates heat associated with the fully-loaded condition even when the motor is only lightly-loaded. The unnecessary production and build-up of heat can be detrimental to the motor itself as well as surrounding components.